Copper sheath MgB₂ wires fabricated by an in situ PIT method

We investigated the applicability of Cu as sheath materials for MgB ₂ wires prepared by in situ PIT (powder-in-tube) method in comparison with stainless steal. Since the critical current density of MgB₂ increases with TiH₂ doping, we prepared TiH₂ doped MgB₂ Cu sheath wires 40 m in length and ∅ 1.0 mm or 0.5×1.0 mm² in cross section by rotary swaging, drawing, and two-axial rolling under cold working. We then annealed the samples at 600-850 °C for 1-2 h in Ar gas atmosphere. The critical current of TiH₂ (6%) doped MgB₂/Cu short sample annealed at 650 °C reached 208 A (J_c=230 kA/cm²) at 4.2 K and self-field. We also fabricated several coils using these wires. The I_c value was ∼100 A at 4.2 K for a coil prepared with use of a 5 m length wire. These results suggest that it is possible to fabricate Cu sheathed MgB₂ wires with good performance by using the in situ PIT method.